1. Field of the Invention
The present invention relates to a redundant apparatus, and in particular to a redundant apparatus which is formed of an active unit and a stand-by unit to which the active unit is switched over when a fault has occurred in the active unit.
In recent years, an information processing system has been made large-sized and complicated increasingly. Especially in a system which works on-line i.e. in real time, a fault partially generated may influence on the whole system to cause a big damage.
To deal with such a fault, there are the art of redundancy to cover the influence of the fault, the art of diagnosing and repairing the fault, and the art in which the former two arts are combined. Among these arts, the art of redundancy is utilized in a redundant apparatus which switches an active unit over to a stand-by unit when a fault has occurred, and diagnoses and repairs the fault to shorten an unavailable time of the system.
In such a redundant apparatus, it has become more and more important to have a restoration speed by which the system has no influence of a fault, and to have an effect for the cost.
2. Description of the Related Art
FIG. 17 shows an arrangement of an electronic switchboard known as the prior art of a redundant apparatus. This apparatus is formed of a circuit equipment DTSH connected to a subscriber 1 and a subscriber 2, and an upper unit 100 connected to this circuit equipment DTSH with a control signal circuit C and main signal circuits A0-A2. The upper unit 100 is formed of a controller 110 connected to the control signal circuit C, a switch portion 120 connected to the main signal circuits A0-A2 and the controller 110, and a diagnosis portion 212 connected to the switch portion 120.
The circuit equipment DTSH is formed of a switch-over portion 300 connected to the subscribers 1 and 2, circuit corresponding equipments (abbreviated as CCE) DT0-DT2 connected to the switch-over portion 300 with the main signal circuits A6-A8 respectively, and a circuit controller DTC which is connected to the circuit corresponding equipments DT0-DT2 with main signal circuits A3-A5 respectively and also connected to the control signal circuit C and the main signal circuits A0-A2.
It is to be noted that the main signal circuits A0, A3, and A6, the main signal circuits A1, A4, and A7, and the main signal circuits A3, A5, and A8 are the same as the main signal circuits A0, A1, and A2, respectively. Therefore, in the following descriptions the main signal circuits A0, A1, and A2 represent the other main signal circuits. Moreover, the main signal circuits A0, A1, and A2 which connect the circuit controller DTC to the switch portion 120 can be one logical circuit as a high way.
In a normal operation, the circuit corresponding equipments DT0, DT1 are preset as an active unit. By the switch-over portion 300, the circuit corresponding equipments DT0 and DT1 are connected to the subscribers 1 and 2, respectively. The circuit corresponding equipment DT2 is preset as a stand-by unit, and is not connected to either of the subscribers 1 or 2. Namely, the equipment DT2 is a stand-by circuit corresponding equipment.
As shown in FIG. 17, the subscriber 1 and the switch portion 120 are fixedly connected with the main signal circuit A0 through the switch-over portion 300, the circuit corresponding equipment DT0, and the circuit controller DTC. In the same way, the subscriber 2 and the switch portion 120 are fixedly connected with the main signal circuit A1 through the switch-over portion 300, the circuit corresponding equipment DT1, and the circuit controller DTC.
The diagnosis portion 212 sends to the stand-by circuit corresponding equipment DT2 a test signal on the main signal circuit A2 through the switch portion 120 and the circuit controller DTC under the control of the controller 110, thereby diagnosing from the response signal whether or not the circuit corresponding equipment DT2 is normal.
FIG. 18 shows an operation example in the case where a fault has occurred in the circuit corresponding equipment DT0 shown in FIG. 17. Having received a notification that the fault has occurred in the circuit corresponding equipment DT0 from the circuit controller DTC, the controller 110 makes the switch-over portion 300 separate the circuit corresponding equipment DT0 from the subscriber 1 in order to withdraw the circuit corresponding equipment DT0 from its active state.
After having instructed the switch portion 120 to set again a passage from the main signal circuit A0 to the main signal circuit A2, the controller 110 makes the switch-over portion 300 connect the stand-by circuit corresponding equipment DT2 to the subscriber 1 for the continuous operation.
Namely, different from FIG. 17, the subscriber 1 will be connected to the main signal circuit A2 through the switch-over portion 300, the stand-by circuit corresponding equipment DT2, the circuit controller DTC, and the switch portion 120.
The controller 110 sets again the passage of the switch portion 120 to connect the diagnosis portion 212 and the circuit corresponding equipment DT0 with the main signal circuit A0. After the circuit corresponding equipment DT0 as faulted is exchanged and repaired, the diagnosis portion 212 sends a test signal to the circuit corresponding equipment DT0 through the main signal circuit A0 by the instruction of the controller 110, thereby diagnosing the circuit corresponding equipment DT0 from the response signal. The result of this diagnosis is sent to the controller 120.
Recognizing from this diagnosis result that the circuit corresponding equipment DT0 has been restored to the normal state, the controller 110 puts the stand-by circuit corresponding equipment DT2 and the restored circuit corresponding equipment DT0 back to the stand-by state and the active state, respectively, and controls the switch portion 120 and the switch-over portion 300 back to the same connection as shown in FIG. 17.
It is to be noted that when the circuit corresponding equipment DT0 is faulted and the stand-by circuit corresponding equipment DT2 is active and the circuit corresponding equipment DT1 is also faulted, the subscriber 2 which is connected to the circuit corresponding equipment DT1 cannot use any circuit corresponding equipment because there is no stand-by circuit corresponding equipment in the stand-by state which is available.
As a measure for this problem, there is a redundant apparatus provided with the plural stand-by circuit corresponding equipments. The function of the redundant apparatus is the same as the redundant apparatus which has only one stand-by circuit corresponding equipment.
In such a prior art redundant apparatus of N+1 type which is formed of e.g. N active circuit corresponding equipments and a single stand-by circuit corresponding equipment, a diagnosis is done by providing N+1 signal systems corresponding to each circuit corresponding equipment. Namely, the main signal circuits like A0-A2 in FIG. 17 are always required for all of the circuit corresponding equipments which should be actually equipped. Therefore, in an electronic switchboard, 1/N of the hardware capacity of the switch portion always remains unused.
The diagnosis of the circuit corresponding equipment requires a function of confirming signal transmissions and receptions by an apparatus including a circuit corresponding equipment DTC in order to return the signal. For this function a hardware resource of the switch portion in the electronic switchboard has been used.
Namely, the diagnosis of the circuit corresponding equipment of the redundant apparatus of the N+1 formation requires the capacity of 1/N to be occupied in respect of hardware and transactions to be made concerning other parts than circuit corresponding equipments as subjected in respect of software.